The present invention relates to a method for concentrating liquid products, such as whey, in particular by vacuum evaporation, as well as a method for crystallisation and drying of the concentrated product.
Furthermore, the present invention relates to a system for concentrating liquid products, and a system for converting a liquid whey product into powder of high quality, such as a free-flowing, non-caking powdery product.
Whey is the liquid by-product of cheese and casein production that remains after the selective coagulation of the casein. Whey contains all of the water-soluble constituents of the milk along with whey proteins, such a lactoglobulins, lactose and some fat.
In the present contest the term whey is used for products selected from acid whey, sweet whey, salt whey, demineralised whey, whey protein fractions, lactose, pure lactose, mother-liquor from lactose crystallisation and similar products.
Permeate is in the present context that portion of a liquid that passes through a membrane when milk or whey is pumped through utltrafiltration systems.
Depending on origin, whey contains 5.5-6.5% total solids, wherein 0.7-0.9% protein, 0.05% fat, 4.2-4.6% lactose and 0.5-1.0% ash. Correspondingly, depending upon origin, permeate contains 4.0-6.0% total solids, wherein 0.2-0.3% protein, 3.3-5.0% lactose and 0.5-0.7% ash.
Concentrated, dried whey products are used for various purposes, such as ingredient in foodstuff for human and animal consumption.
In prior art several processes are known for converting liquid products, such as whey and permeate into free-flowing, non-caking powdery products.
In these known processes the liquid product is initially concentrated as much as possible, such as in a multiple effect falling film tubular evaporator. Thereby a concentration of whey up to 50-65% of total solids (TS) can be obtained.
This liquid product with 50 to 65% total solids may thenxe2x80x94in a process commonly carried out by industryxe2x80x94immediately after evaporation be cooled slowly batchwise in large tanks provided with slow moving agitators for crystallisation of lactose. After crystallisation the concentrate is spray dried to its final moisture content and cooled in a fluid bed. (Masters, Spray Drying Handbook, 4 ed. 1985, p.596)
Another similar prior art process provides multiple crystallisation stages. (Masters, Spray Drying Handbook, 4 ed. 1985, p.597, FIGS. 15,12). A first crystallisation stage is obtained in large tanks as just described above. The concentrate is then spray dried to a moisture content of about 10 to 12% and the moist powder is left on a continuous belt conveyer for final crystallisation. The product is then milled and dried to its final moisture in a fluid bed. In this way a, free flowing, non-caking powder may be obtained.
In a more recent described procedure (U.S. Pat. No. 5,006,204, Niro Atomizer) the belt is substituted by a slowly rotating disk to receive partially dried whey powder from the spray dryer and deliver it to the fluid bed while permitting time for crystallisation.
The mentioned prior art processes all have several drawbacks. First, the energy efficient multiple effect evaporation process can only be used to concentrate the whey to 50 to 65% TS while the rest of the water removal requires a less energy-efficient air dryer.
Second, the known processes put severe limits to the operator""s choice process parameters: It is well known to the person skilled in the art of multiple effect evaporators, that relatively high product temperatures towards the end of the concentration process are desirable, because they effectively reduce the content of micro-organisms and reduce viscosity. However, the same relatively high product temperatures promote the formation of Maillard reaction products and causes unacceptable browning and discoloration of the final product.
It is also well known, that a solution of lactose in water is able to form a super saturated solution up till approx. 2 times its solubility. This limit is already met in prior art evaporators and attempts to produce concentrates with higher total solids by using acceptable low temperature levels will therefore unavoidably lead to formation of large amounts of lactose crystals within the evaporator. This leads to scaling and very high viscosities and unpumpable products.
Third, the prior art dictates use of belts, rotating disks or discontinuously-operating crystallisation tanks, i.e. large, space and labour requiring equipment.
EP 205 601 (APV Anhydro) describes yet another process for production of a substantially free-flowing, non-caking powdery product from whey, whereby the whey is concentrated to 75% TS in vacuum evaporators. Thereafter the concentrate is passed once through a heat exchanger for cooling and crystallisation. The whey paste, which now has a high content of alpha monohydrate lactose, is fed to a Spin Flash dryer which converts the paste into a dry non-caking powder. The Spin Flash dryer is described in e.g. EP 141403 (APV Anhydro)
It has been found, however, that the whey paste from the evaporator in this process becomes extremely high viscous and very difficult to disintegrate in the spin flash dryer at elevated temperatures. Therefore, this process only allows for relatively low drying temperatures, which makes it very energy inefficient. The process has not been implemented by the whey-processing industry.
Therefore, since long the whey and permeate industry has an unfulfilled demand for a new process for converting liquid products, such as whey and permeate into a substantially free-flowing, non-caking powdery product, and which process is more energy efficient than the prior processes implemented by industry and at the same time provides an apparatus requiring much lesser building volume than the previous apparatuses.
The present invention relates to a method for concentration of a liquid product said liquid product having a dry solid content of at least 40% and said liquid product comprising crystallizable components, comprising the steps of heating the liquid product to a temperature above the crystallisation temperature of the liquid product in a heat exchanger, transferring the heated liquid product to a separator, flash separating volatile components from said heated liquid product and obtaining a liquid concentrate of the liquid products. By the present invention it has been possible to concentrate the liquid product to a very high concentration of solids, avoiding crystallisation of the liquid product during heating and separation. By the term xe2x80x9ccrystallisation of the liquid productxe2x80x9d is meant crystallisation of crystallizable components in the liquid product. Furthermore, by the present invention it is possible to concentrate a liquid product having a high starting content of solids, i.e. at least 40% of solids. The content of solids relates to the content of total dry solids (TS) as described below. Accordingly, the present invention offers a cost-effective method of concentrating a liquid already having a high content of solids. The method is particularly effective to apply after state of the art concentration processes described above and before drying processes.
The crystallisation temperature is depending on the concentration of solids in the liquid product. By the term xe2x80x9ca temperature above crystallisation temperaturexe2x80x9d is meant the temperature at which substantially no crystallisation occurs when the liquid product is flowing in the concentration system, at the predetermined solid concentration of the liquid product. In particular substantially no formation of x-lactose crystals occurs when the liquid product is heated to the temperature above crystallisation temperature.
In particular the present method may be applied for concentration of liquid whey products, whey products being as defined elsewhere in the description.
In the present context the term xe2x80x9cliquid productxe2x80x9d is meant to define the starting material fed into the concentration system, whereas the term xe2x80x9cliquid concentratexe2x80x9d is meant do define the product obtained after flash separation.
Furthermore, the invention relates to a method of converting whey into substantially free-flowing, non-caking powdery product comprising the steps of, subjecting whey to concentration as defined above obtaining a main stream of liquid whey concentrate, crystallisation of the whey concentrate and drying said crystallised whey obtaining free-flowing, non-caking powder. The powder flowability may be measured according to Cheremisinoff (see below) whereby a free-flowing powder is having an angle of repose of 30 or less. The caking properties are estimated by examining the crust formed on a spoonful of powder, subjected to 60% relative humidity at 20xc2x0 C. for 24 hours. A non-caking powder does not form any crust under these conditions. A non-caking powder is more stable than caking powders.
When the concentration process is carried out according to the invention a powder having very good properties in relation to flowability and cakability is obtained.
By the term a powdery product is meant a product normally considered as powder, i.e. having a particle size corresponding to powder, such a preferably above 0.1 xcexcm and preferably below 2 mm. The particle size is measured as the approximate diameter of the particle.
By the methods according to the invention the concentration, crystallisation and drying of liquid products may be carried out in a system which is more energy efficient and requires less building volume than prior art systems.
Accordingly, the present invention further relates to a system for concentrating liquid products, having a concentrating unit comprising means for feeding an inlet of a heat exchanger, a heat exchanger comprising at least one inlet and one outlet, connecting means for connecting the heat exchanger outlet and an inlet of a separator vessel, and a separator vessel, comprising at least one inlet and least two outlets.
Furthermore, the invention relates to a system for converting whey into a powdery product comprising means for concentration of a liquid product as defined above, means for initial crystallisation of the liquid concentrate, and means for drying said crystallised product obtaining free-flowing, non-caking powder, which means are interconnected by a main conduct.
The system provided by the present invention provides for a rapid and economic production of high quality powder from a liquid product.